Abstract
This paper proposes a discrete-time sliding mode (DTSM) controller designed for dc-link voltage control for quasi-Z source inverter (q-ZSI) employed in a 3-phase grid-tied photovoltaic system. The dc-link voltage control of q-ZSI offers non-minimum phase behavior, which complicates the controller design. The proposed DTSM controller is separately employed to regulate dc-link voltage in the outer loop and inductor current control in the inner loop. Thus, the dc-link voltage control of q-ZSI is achieved with the proposed DTSM controller-based dual-loop control. In the outer voltage control loop, the DTSM controller determines the reference inductor current for the inner current control loop and the inner current control loop further determines the shoot-through duty ratio. The discrete-time model of q-ZSI is developed for the derivation of the proposed DTSM based control law. The designed DTSM controller offers advantages in terms of simplified discrete implementation, robustness, and achieves good steady-state and dynamic operating conditions. The effectiveness of the proposed DTSM controller is assessed with twenty-six different operating conditions with ideal and non-ideal grid conditions as well as balanced and unbalanced loading. The results reveal that the q-ZSI-based 3-phase grid-tied photovoltaic(PV) system operation with the proposed DTSM controller results in IEEE-1547 compliant operation with active power injection and sinusoidal currents supplied by the inverter.